1. Field of the Invention
The present invention relates to a controller for an internal combustion engine, more particularly to a controller for controlling a waveform of a current supplied to a solenoid in the internal combustion engine which has a fuel injection system with the solenoid.
2. Prior Art
Conventionally, a fuel injection valve (injector) which injects the fuel into the combustion chamber of the internal combustion engine includes therein a plunger, a solenoid for energizing the plunger in a valve opening direction, and a spring for energizing the plunger in a valve closing direction. The fuel injection valve is supplied with a high fuel pressure which energizes the plunger in a valve opening direction.
The solenoid (injector) is supplied with a driving current which is generated by a battery and has a single waveform of current. A fuel injection from the fuel injection valve into the combustion chamber of the internal combustion engine is controlled by the driving current of the single waveform. The driving current is supplied to the solenoid in response to a signal applied to the solenoid in the fuel injection valve from a controller.
For example, Japanese Application Patent Laid-open Publication No. Hei 11-13519 and Japanese Application Patent Laid-open Publication No. Hei 11-343910 disclose a solenoid supply control for the fuel injection from the fuel injection valve. In the control, the driving current for the fuel injection valve (injector) has a single waveform having two current stages consisting of one stage of a valve opening signal and one stage of a holding current. A fuel injection pulse width is changed by the driving current according to the operating condition of the internal combustion engine. Thus, the amount of the fuel injection into the combustion chamber of the internal combustion engine is controlled to control the combustion in the internal combustion engine.
Recently, the fuel injection valve (injector) mounted in the internal combustion engine has been strongly required to be smaller to meet the various demands. However, a smaller fuel injection valve (injector) will result in a smaller inductance of the solenoid included in the fuel injection valve (injector). Thus, the solenoid may generate a smaller magnetmotive force with the above described conventional current of a single waveform applied to the solenoid and may generate a smaller suction force of the plunger in the fuel injection valve (injector). In particular, when a fuel is provided at a higher pressure, the solenoid may sometimes not generate a sufficient magnetmotive force for the suction of the plunger and the fuel injection valve may not inject the fuel.
It is also very important how minimum amount of fuel the injection valve (injector) can inject per injection, in other words, the property of minimum amount of fuel per injection of the fuel injection valve. The property of minimum amount of fuel is particularly required in the stratified charge lean combustion and is very important for the fuel efficiency and emission characteristics.
It is an object of the present invention to provide a controller for an internal combustion engine having a fuel injection system, which can realize an optimum injection even with a smaller inductance of a solenoid due to a smaller fuel injection valve (injector) and has a good property of minimum amount of fuel injection.
To achieve the above described object, a controller of the internal combustion engine according to the present invention is basically a controller for an internal combustion engine having a fuel injection system with a solenoid comprising: a detection system for detecting an operating condition of the internal combustion engine; a means for calculating a fuel injection pulse width according to the above described detected operation condition; and a solenoid control means, wherein the above described solenoid control means comprises, a means for supplying the above described solenoid a valve-opening current up to a large predetermined current value according to the above described calculated fuel injection pulse width; a means for supplying the solenoid a holding current for holding a valve opening state, after the above described valve-opening current has reached the predetermined current value; and a current waveform control means for forming a plurality of different current waveforms to be supplied to the above described solenoid and switching between the different current waveforms according to the above described detected operating condition.
According to one specific aspect of the present invention, the solenoid control means comprises, a boost circuit for boosting power from a battery; a first switching circuit for supplying the power from the above described boost circuit to the above described solenoid; a second switching circuit for supplying the power from the above described battery to the above described solenoid; a third switching circuit for sinking current from the above described solenoid to the ground; and a flywheel circuit for cycling current from the ground through the above described solenoid and the above described third switching circuit to the ground when the above described first switching circuit and the above described second switching circuit are off.
According to another specific aspect of the present invention, the above described plurality of current waveforms supplied to the above described solenoid have three types of current waveforms consisting of a first current waveform having one stage of a valve-opening current and two stages of a holding current; a second current waveform having one stage of a valve-opening current and one stage of a holding current; and a third current waveform having one stage of a valve-opening current and one stage of a holding current, the third current waveform being different from the above described second current waveform.
The controller for an internal combustion engine configured as described above according to the present invention can optimally control the injector even with a smaller inductance of the solenoid in the above described injector due to the smaller size of the injector and can hold a good property of minimum amount of fuel.
According to another specific aspect of the present invention, the above described current waveform control means forms the above described first current waveform by turning on the above described first switching circuit and the above described third switching circuit to supply a valve-opening current up to a large predetermined current value, then turning off the above described first switching circuit and turning on/off the above described second switching circuit to supply a large holding current which holds a valve opening state for a predetermined time using the above described flywheel circuit, and turning on/off the above described second switching circuit to supply a small holding current which holds a valve opening state for a predetermined time using the above described flywheel circuit.
According to still another specific aspect of the present invention, the above described current waveform control means forms the above described second current waveform by turning on the above described first switching circuit and the above described third switching circuit to supply a valve-opening current up to a large predetermined current value, and turning off the above described first switching circuit and turning on/off the above described second switching circuit to supply a small holding current which holds a valve opening state for a predetermined time using the flywheel circuit.
According to still another specific aspect of the present invention, the above described current waveform control means forms the above described third current waveform by turning on the above described first switching circuit and the above described third switching circuit to supply a valve-opening current up to a large predetermined current value, then turning off the above described first switching circuit and the above described third switching circuit to reduce switching time from the valve opening current to the holding current, and turning on the third switching circuit and turning on/off the above described second switching circuit to supply a small holding current which holds a valve opening state for a predetermined time using the flywheel circuit.
According to still another specific aspect of the present invention, the above described current waveform control means switches between at least two types of the three types of current waveforms supplied to the above described solenoid according to the detected operation condition of the above described internal combustion engine.
According to still another specific aspect of the present invention, the above described controller comprises a means for controlling a pressure of fuel supplied to the above described fuel injection system; and a means for detecting the above described fuel pressure, wherein the above described operating condition is indicated in the above described fuel pressure, and the above described controller comprises means for comparing the fuel injection pulse width calculated by the above described fuel injection pulse calculating means with a minimum effective fuel injection pulse width, and the above described operating condition is indicated in the above described comparison results, and the above described controller protects switching between the above described current waveforms supplied to the solenoid during the fuel injection.
According to still another specific aspect of the present invention, the above described controller comprises an arithmetic unit for determining the operating condition of the above described internal combustion engine, wherein the above described arithmetic unit and the above described current waveform control means are connected via serial communication.